A variety of work machines such as, loaders, excavators, motor graders, and other types of construction, work, and earth moving machinery use one or more hydraulically actuatable implements for accomplishing a task. These hydraulically actuatable implements may be operated by a hydraulic actuator, such as, a cylinder and a piston assembly. The cylinder may be in fluid communication with a hydraulic pump for providing pressurized fluid to the chambers thereof, as well as in fluid communication with a fluid source or a tank for draining pressurized fluid therefrom. A valve arrangement may be connected between the pump and the cylinder and/or between the cylinder and the fluid source to control the flow rate and direction of pressurized fluid to and from the chambers of the cylinder.
The rate of flow through the hydraulic valve may be dependent upon a hydraulic pump flow (that is, available fluid flow from the pump). For example, an operating hydraulic pump (e.g., partially upstroked) can typically provide a consistent flow of hydraulic fluid. Whereas a hydraulic pump that is not currently operating at full capacity will typically have a delayed flow of fluid (due to hydraulic pump upstroke) as it is started, speeded up, or the like. As the pump flow varies, the fluid flow through the hydraulic valve may vary.
Implement response is a critical performance criteria and is subject to the available fluid flow from the pump. Therefore, the response of an implement hydraulically controlled by an input command may vary depending upon the state of the hydraulic pump. For example, for a given input command, an implement response may be delayed by hydraulic pump upstroke (hydraulic pump starting). This not only affects the time taken to accomplish a task, it also affects the productivity of the operator who has to continuously account for the variations in pump operation when issuing input commands to achieve performance from the implement. Moreover, implement response may be even further critical in automated applications as these applications may not fully compensate for a delayed response.
One control apparatus for a hydraulic excavator is disclosed in U.S. Pat. No. 5,999,872. In this patent, a control apparatus for a hydraulic excavator is capable of carrying out precise operations according to various kinds of classifications of works. The apparatus includes a classification of work discriminating section for recognizing a classification of work being carried out by the hydraulic excavator on the basis of data detected by sensors for detecting an operating amount of a lever for a boom and the like. The apparatus includes sections for setting an operating mode of hydraulic pumps absorbing horse power and the like, according to the classification of work recognized. The apparatus includes a hydraulic pump control section for controlling the hydraulic pumps according to the set operating mode and an auto acceleration control section for making effective or invalid the auto acceleration control for controlling speed of an engine to a low speed when work stops.
It would accordingly be beneficial to have a mechanism to control the fluid flow through a hydraulic valve and associated operation of a pump in order to have improved performance of the hydraulic system.